The present invention relates to systems that simultaneously constitute both emitters and receivers of optical signals over an optical fiber.
There is a desire at present to make use of optical fibers in ever more numerous and varied applications.
Thus, it is desired to be able to use a single optical fiber to convey signals of different kinds, such as telephone signals, television signals, or indeed signals carrying computer data. In conventional manner, the signals of different kinds conveyed in the same fiber are given different respective wavelengths so as to enable the signals to be distinguished from one another.
Thus, it is necessary to be able to use a single optical fiber to convey multiple signals simultaneously, including signals propagating in opposite directions, and it is necessary to be able to perform various different operations at an end of the optical fiber.
A first operation is controlling both-way communications over the optical fiber, such as a telephone call, for example.
A second operation is to separate various signals reaching said end, as a function of their wavelengths.
In addition to both-way communications, provision may be made at the end of the fiber to receive a plurality of signals of different wavelengths, such as, for example., a television signal and a signal carrying computer data.
A third operation is multiplexing various signals. This operation is necessary when it is desired to inject various signals of different kinds into the fiber.
For the first operation, proposals are made in xe2x80x9c1.31-1.55 xcexcm phase array demultiplexer on InPxe2x80x9d by R. Mestric, H. Bissessur, D. Martin, and A. Pinquier, published in IEEE Photonic Technology Letters, Vol. 8, No. 5, May 1996, to use a spectrograph or xe2x80x9cgratingxe2x80x9d comprising an array of waveguides (also known as a xe2x80x9cphasarxe2x80x9d) that has an xe2x80x9cinletxe2x80x9d channel on a first coupler and two xe2x80x9coutletxe2x80x9d channels on a second coupler, and to connect the two xe2x80x9coutletxe2x80x9d channels respectively to a laser and to a photodetector.
The inlet channel is connected to an optical fiber, and the role of the phasar is to inject into the fiber signals which the phasar receives on a first xe2x80x9coutletxe2x80x9d channel, and to inject into its other xe2x80x9coutletxe2x80x9d channel the signals it receives from the optical fiber.
That system is restricted to two wavelengths that are relatively far apart, i.e. equal to 1.33 xcexcm and 1.55 xcexcm, and it is not capable of separating wavelengths that are separated by differences of less than 0.04 xcexcm, as would otherwise be desirable for both-way communications such as telephone calls.
Thus, that system cannot provide both-way communications at 1.28 xcexcm and at 1.32 xcexcm.
Concerning the first operation, proposals have also been made in xe2x80x9cHorizontal directional coupler filter suitable for integration in a 1.3+/1.3xe2x88x92 xcexcm duplexerxe2x80x9d by S. Francois, M. Filoche, F. Huet, S. Fouchet, G. Hervxc3xa9-Gruyer, A. Ougazzaden, J. Brandon, N. Bouadma, M. Carrxc3xa9, and A. Carenco, published in Electronics Letters, Vol. 31, No. 23, Nov. 9, 1995, to make a meandering directional coupler enabling both-way communications to be managed in a telecommunications window situated around a wavelength of 1.3 xcexcm. In order to separate two wavelengths respectively of 1.28 xcexcm and 1.32 xcexcm with good crosstalk between the arms of the coupler, use is made in that case of a Hamming function to vary a coupling coefficient along a propagation direction.
For systems that are small enough in size to be acceptable, directional couplers present the major drawback of being capable of achieving good crosstalk levels only over particularly narrow wavelength zones. For numerous applications requiring systems for interchanging optical signals, those systems therefore do not make it possible to work over wavelength zones that are sufficiently large.
Furthermore, those systems present the drawback of being particularly difficult to implement.
Concerning the second operation, it is known that a phasar can be used having an inlet channel connected to the optical fiber, and outlet channels connected to receivers where the phasar is adapted to separate signals of different wavelengths reaching the phasar via the fiber, and to deliver them to corresponding receivers connected to the various outlet channels.
Proposals have also been made in xe2x80x9cDemonstration and application of a monolithic two-PONs-in-one devicexe2x80x9d by Yuan P. Li, L. G. Cohen, C. H. Henry, E. J. Laskowski, and M. A. Cappuzzo, of Lucent Technologies, Bell Laboratories, at the 22nd European Conference on Optical Communication, for a system comprising Mach-Zender type elements making it possible, starting from a multiwavelength signal comprising eight channels at 1.5 xcexcm and one channel at 1.3 xcexcm, to subdivide the 1.3 xcexcm channel and to demultiplex the signals at 1.5 xcexcm. That system has eight outlet fibers, each of which delivers a respective portion of the 1.3 xcexcm signal together with one of the eight channels at 1.5 xcexcm.
Mach-Zender type systems suffer from the same drawbacks as both-way couplers. They enable good cross-talk to be obtained only over particularly narrow wavelength zones, and they are particularly difficult to make.
Those various systems also suffer from the major drawback of performing only one of the three above-mentioned operations that may be necessary at one end of an optical fiber. Thus, at a given end of a fiber, they do not enable both-way communication to be provided simultaneously with wavelength separation of signals arriving over the fiber, or both-way communication with multiplexing of signals to be injected into the fiber.
For example, the simple systems that have been proposed in the past do not enable a single optical fiber to receive and emit telephone signals while simultaneously receiving a television signal.
An object of the present invention is to mitigate those various drawbacks and to provide a system that is simple to make, and that is suitable for performing those various operations at one end of an optical fiber.
According to the present invention, those objects are achieved by a system for interchanging optical signals over an optical fiber, the system comprising an optical component of the spectrograph type having an array of waveguides extending between two couplers, and channels extending from the couplers to the outside of the component, said system also comprising an optical signal emitter and an optical signal receiver, a channel of one of the couplers of the optical component being connected to the optical fiber, a first channel and a second channel of the other coupler of the optical component being respectively connected to an inlet of the receiver and to an outlet of the emitter, wherein said other coupler has a third channel connected to a port of another optical component of the system.